A control device of a steering gear of a ship is generally composed as follows; namely, as shown in FIG. 10, an auto-pilot steering apparatus 51 has two steering order systems of an automatic steering system 52 and a hand steering system 53; a steering gear 55 for operating a rudder 54 is operated by a No. 1 hydraulic pump unit 56a or a No. 2 hydraulic pump unit 56b, respectively provided independently; and the No. 1 hydraulic pump unit 56a and the No. 2 hydraulic pump unit 56b are controlled by a No. 1 control amplifier 57a and a No. 2 control amplifier 57b, respectively.
An actual turning angle of the rudder 54, namely, the steering gear 55, is detected by a No. 1 rudder angle detector 58a and a No. 2 rudder angle detector 58b, respectively, and a signal of an actual turning angle is fed back to the No. 1 control amplifier 57a and the No. 2 control amplifier 57b, respectively, for follow-up control. In this context, the No. 1 control amplifier 57a can be changed over for controlling the No. 2 hydraulic pump unit 56b, and the No. 2 control amplifier 57b can be changed over for controlling the No. 1 hydraulic pump unit 56a. 
Furthermore, as other means of controlling the steering gear 55, a non-follow-up steering system 59 for operating the No. 1 control amplifier 57a and the No. 2 control amplifier 57b without follow-up control directly from a bridge, and a device for manually operating the No. 1 hydraulic pump unit 56a and the No. 2 hydraulic pump unit 56b at the steering gear site are provided. Besides, an actual turning angle of the rudder 54 is detected by a rudder angle transmitter 60, and indicated at a rudder angle indicator 61.
When a certain rudder angle order signal δi is emitted from the automatic steering system 52 or the hand steering system 53 of the auto-pilot steering apparatus 51, this signal is input into the No. 1 control amplifier 57a or the No. 2 control amplifier 57b wherein this signal is amplified and a control signal δc is output. The control signal δc controls the No. 1 hydraulic pump unit 56a or the No. 2 hydraulic pump unit 56b, and operates the steering gear 55 and the rudder 54.
A turning angle of the rudder 54, namely, the steering gear 55, is detected by the No. 1 rudder angle detector 58a and the No. 2 rudder angle detector 58b, and the turning angle signal is fed back to the No. 1 control amplifier 57a and the No. 2 control amplifier 57b, respectively, as a rudder angle feed-back signal δf. Respectively in the No. 1 control amplifier 57a and the No. 2 control amplifier 57b, the rudder angle order signal δi and the rudder angle feed-back signal δf are compared, and, when it comes to such a state as δi=δf, the No. 1 control amplifier 57a or the No. 2 control amplifier 57b stops operation of the No. 1 hydraulic pump unit 56a or the No. 2 hydraulic pump unit 56b, and the steering gear 55, namely, the rudder 54, is held at the ordered rudder angle (namely, the rudder angle corresponding to the rudder angle order signal δi).
In the aforementioned control device of a steering gear 55, rudder angle detecting mechanism is composed as shown in FIG. 11˜FIG. 13 in case of a rotary vane type steering gear. Namely, a steering gear rotor 63 that is a body rotating together with a rudder-stock 62 is bound with the rudder-stock 62, and the binding is fixated by a nut 64. On the upper surface of the nut 64, a stand 65 is provided, the turning center CS of which coincides with the axis CR of the rudder-stock 62, and a yoke 66 is fitted on the upper surface of the stand 65. The yoke 66 has two ramifications 66a, 66b. 
On the other hand, a casing top cover 67 of the steering gear 55, which is an unrotating structural body, fixedly holds on its surface the No. 1 rudder angle detector 58a and the rudder angle transmitter 60 so that they are operated by the first ramification 66a of the yoke 66, and the No. 2 rudder angle detector 58b so that it is operated by the second ramification 66b of the yoke 66, respectively. A yoke pin 68 is provided at a pointed end of the first ramification 66a of the yoke 66, the yoke pin 68 being connected with a pointed end of a lever 69 of the No. 1 rudder angle detector 58a by a connecting rod 70, and at the same time, the yoke pin 68 being connected with a pointed end of a lever 71 of the rudder angle transmitter 60 by a connecting rod 72. Furthermore, a yoke pin 73 is provided at a pointed end of the second ramification 66b of the yoke 66, the yoke pin 73 being connected with a pointed end of a lever 74 of the No. 2 rudder angle detector 58b by a connecting rod 75.
As shown in FIG. 11, turning arm length of the yoke pin 68 (namely, distance from the turning center CS to the center of the yoke pin 68) is same as the length of the lever 69 of the No. 1 rudder angle detector 58a, and the length of the lever 71 of the rudder angle transmitter 60. Furthermore, turning arm length of the yoke pin 73 (namely, distance from the turning center CS to the center of the yoke pin 73) is same as the length of the lever 74 of the No. 2 rudder angle detector 58b. The respective connecting rods 70, 72, 75 are of such construction as to be adjustable of the connecting length, and hereby adjustment is conducted so that the turning arm of the yoke pin 68 (namely, the first line L1 passing through the turning center CS and the center of the yoke pin 68) becomes parallel with the lever 69 of the No. 1 rudder angle detector 58a, and the lever 71 of the rudder angle transmitter 60, respectively, and that the turning arm of the yoke pin 73 (namely, the second line L2 passing through the turning center CS and the center of the yoke pin 73) becomes parallel with the lever 74 of the No. 2 rudder angle detector 58b. 
In this context, in case of a ram-type or a piston-type steering gear, such a yoke is provided on a rudder-stock or a tiller, and rudder angle detectors and a rudder angle transmitter are provided on a deck, but mechanism of connecting both is similar to that of the case of a rotary vane type steering gear aforementioned.
Furthermore, the steering gear 55 is provided with limit switches that independently function for the No. 1 control amplifier 57a and the No. 2 control amplifier 57b, respectively, so that the rudder 54 is prevented from moving beyond the respective maximum rudder angles limits by reason of erroneous function of feed-back control mechanism, etc. In case that it is so arranged that the steering gear 55 works within the maximum rudder angle limits of 35°-45° port and 35°-45° starboard, for example, for navigation mode, and within the maximum rudder angle limits of 70° port and 70° starboard, for example, for harbor operation mode, the respective limit switches for limiting a rudder angle at 35°-35° (or 45°-45°) and the respective limit switches for limiting a rudder angle at 70°-70° are independently provided. And, though figuring is omitted, these limit switches are randomly arranged at exteriorly exposed moving portions of the steering gear 55.
The rotary vane steering gear 55 makes it one of special characters as inherent properties of its main body that no protruded moving portion exteriorly exposes, which makes safe operation possible, and that it gives excellent aesthetic sense with its simple cylindrical external form. However, the steering gear 55 necessitates that the mechanism for detecting a rudder angle (including the limit switches) is appended to the main body of the steering gear 55, and, with a conventional manner, as shown in FIG. 11-FIG. 13, there have been such problems that these appendages form the protruded moving portions exteriorly exposed (the yoke 66, the levers 69, 71, 74, the connecting rods 70, 72, 75, etc.), which spoil the features of safe operation and the aesthetic sense inherent in the steering gear 55. Furthermore, there have been such ill-conditions that the aforementioned mechanism for detecting a rudder angle (including the limit switches) is apt to be affected by contaminated environment, and happens to cause ill-operation by an accidental mechanical blow sustained during work because of its exposure to the exterior of the steering gear 55.
Furthermore, in the aforementioned constitution, when the casing top cover 67 is removed, or the nut 64 that fixates bond between the rudder-stock 62 and the steering gear rotor 63 is removed and fitted, for overhaul inspection of the steering gear 55, the connection between the yoke 66 and the respective rudder angle detectors 58a, 58b and rudder angle transmitter 60 must be disconnected by removing the connecting rods 70, 72, 75. Accordingly, when they are re-assembled, in order to make it possible that a rudder angle is accurately transmitted to the rudder angle detectors 58a, 58b and the rudder angle transmitter 60, length of the respective connecting rods 70, 72 must have been minutely adjusted, so that the No. 1 rudder angle detector lever 69 and the rudder angle transmitter lever 71 come to accurately parallel the aforementioned first line L1, collating with an actually indicated rudder angle, with the steering gear 55 being operated. Similarly, length of the connecting rod 75 must have been minutely adjusted so that the No. 2 rudder angle detector lever 74 comes to accurately parallel the aforementioned second line L2, collating with an actually indicated rudder angle, with the steering gear 55 being operated. Such work for adjusting length of the respective connecting rods 70, 72, 75 is considerably troublesome, and there has been a problem that the re-assembling/re-adjusting work requires much labor and time.
Furthermore, in case that it is required for the steering gear 55 to take a large rudder angle (for example, 70° port and 70° starboard), there has been a problem that, in the condition of the 70° rudder angle (a large rudder angle), accurate transmission of a rudder angle to the rudder angle detectors 58a, 58b and the rudder angle transmitter 60 becomes hard because, with a large rudder angle, an angle made by the connecting rod 70 and the No. 1 rudder angle detector lever 69, and an angle made by the connecting rod 72 and the rudder angle transmitter lever 71, and an angle made by the connecting rod 75 and the No. 2 rudder angle detector lever 74 becomes small geometrically to the extreme degree, and furthermore, adjustment of length of the connecting rods 70, 72, 75 becomes further troublesome and delicate for such a large rudder angle.
Furthermore, in the light of such a phenomenon that there is a case that the rudder-stock 62 suffers off-centering motion by reason of abrasion of an upper radial bearing 76 provided between the rotor 63 and the casing top cover 67 of the steering gear 55 or a lower radial bearing (illustration is omitted), and ill-alignment at installation work, etc., a certain consideration is given design-wise so that the connection between the moving portions and the stationary portions in the rudder angle detecting mechanism allows such off-centering motion. There has been a problem, however, that enlargement of a rudder angle detecting error by off-centering motion is unavoidable.
The present invention resolves the aforementioned problems and aims at offering such a rudder angle detecting device of a steering gear as to make possible of safe operation of a steering gear by dispensing with protrusive moving portions that exteriorly protrude from a steering gear; make a steering gear excellent in aesthetic sense inherent in a rotary vane type steering gear; make troublesome readjusting work for detecting a rudder angle unnecessary at the time of overhaul inspection and reassembling of a steering gear; make a degree of the precision of detecting a rudder angle unvaried regardless of magnitude of a rudder angle; dispense with hardness of adjustment for detecting a large rudder angle; and furthermore, bring no ill-condition in the rudder angle detecting mechanism and is correctly detectable of a rudder angle even in case of off-centering motion of a rudder-stock.